Hybrid powertrain systems are configured to manage input and output torques of various prime-movers in hybrid vehicles, such as internal combustion engines and electric machines. In some hybrid powertrain architectures, the internal combustion engine drives an electric generator, which in turn provides electrical power to an electric drivetrain and to a battery pack. The electric generator may also provide a starting function to the internal combustion engine, and the electric drivetrain may recapture vehicle braking energy to recharge the battery pack. In other configurations, the internal combustion engine and an electric motor are directly mechanically coupled to the drivetrain, which includes a shifting transmission to provide suitable gear ratios, such as variable speed ratios, for a wide range of operations.
To provide continuously variable speed ratios, the powertrain may include an electrically variable transmission (EVT). Generally, an EVT is operable with a direct mechanical path between an internal combustion engine and a final drive unit to thereby enable high transmission efficiency. EVTs can also operate mechanically independently from the final drive unit and may be able to operate in various mechanical/electrical split contributions to enable high-torque continuously variable speed ratios, electrically dominated launches, regenerative braking, engine off idling, and multi-mode operation.
An amount of power to drive the internal combustion engine may be selected based on a road-load demand and on a state-of-charge of the battery pack. Following selection of the engine power amount, the engine's optimal fuel economy or optimal emissions map or a combination thereof may be used to select a torque/speed operating point for the engine. The battery pack may output additional power, in combination with the engine power, to meet the road-load power demands and to compensate for power losses within the hybrid powertrain system.
Although the aforementioned hybrid powertrain architectures generally operate suitably in most circumstances, they may be improved. For example, power output by the battery pack may not operate as intended when exposed to extremely cold temperatures (e.g., below about 0° C.). In particular, the state-of-charge of the battery pack may be affected by such temperatures, and the battery pack may not be capable of meeting the power demands of the powertrain and/or the EVT under such conditions.
Accordingly, it is desirable to have an improved hybrid powertrain architecture that is capable of operating in temperatures of at least 0° C. or below. Furthermore, other desirable features and characteristics of the inventive subject matter will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.